Aleksandar Kolarov has claimed that "nobody knows who to mark" at set-pieces in Manchester City's controversial zonal-marking system but the defender believes that Roberto Mancini's side still have what it takes to go through the season unbeaten.

The Premier League champions conceded twice from corners in last week's 2-2 draw against Ajax and trailed to Tottenham on Sunday when Steven Caulker headed in Tom Huddlestone's free kick, before fighting back to win 2-1.

Of the goals City have let in this season, 60% have come from corners and free-kicks and Kolarov said this is down to confusion among the players about who they should be picking up at dead-ball situations.

"We need to improve on set-pieces because we conceded two goals against Ajax in the Champions League and then another on Sunday," Kolarov told the Manchester Evening News.

"We mark from zone to zone and nobody knows who needs to mark the player. We need to improve on this, but we reacted very well to being a goal down, which is always important."

But despite City's defensive difficulties, Kolarov believes they are still the Premier League's finest team and thinks they could prove unbeatable this season.

Mancini's side have the division's only undefeated record and Kolarov is impressed by the character they displayed against Spurs.

"We need to improve on our performance against Tottenham, and in training, but we are going down the right road and if we keep getting better it could be good at the end of the season," the Serbian said.

"I understand why we get so much criticism. Everybody wants to beat us because we are the champions and haven't lost any games this season.

"The smallest teams, and the biggest teams, all want to beat us and give 200% to do that. We have lost games in the Champions League but we are still the best team in the Premier League, I think.

"If we play the way we know how, we will be the champions. If we carry on playing with the same spirit we showed against Spurs, nobody can beat us."